


Constants and Variables

by meganphntmgrl



Category: The Avengers (Marvel Movies), Thor (Movies)
Genre: Alternate Universe - Canon Divergence, Alternate Universe - Role Reversal, Character Death, Family Drama, Gen
Language: English
Status: In-Progress
Published: 2013-11-04
Updated: 2013-11-10
Packaged: 2017-12-31 13:11:28
Rating: Teen And Up Audiences
Warnings: Graphic Depictions Of Violence
Chapters: 3
Words: 4,206
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/1032082
Author URL: https://archiveofourown.org/users/meganphntmgrl/pseuds/meganphntmgrl
Summary: <blockquote class="userstuff">
              <p>There is always a broken bridge and a falling prince, but sometimes the players trade roles.</p>
            </blockquote>





	1. Then

**Author's Note:**

> This story was prompted by a request on Norsekink for an AU in which Thor, rather than Loki, is the son who falls from grace. 
> 
> At first, I wasn't sure how this could work- I've commented a few times whenever the subject of an AU where Thor is the adopted frost giant in the family and Loki is the biological son of Odin that the only real difference would be "because no matter how much you claim to love me, you'd still rather have a _frost giant_ on the throne of Asgard!" I think there's a lot of twisted-up bitterness inside of Loki that really does mean he'd never be the golden son, no matter what happened to Thor. 
> 
> However, so much of the prompt hung on the fact that the prompter wanted Thor to still love Loki even after his fall, and that, I think, is what made me start sketching out the story in my head. The idea of their core personalities remaining in place even as they wound up on opposite sides of the moral equation relative to their canon fates made this a lot more interesting a challenge to me as a writer than simple villain!Thor and hero!Loki. 
> 
> So here it is. I hope you enjoy it.

It is easy to forget how much difference only a few seconds might make.  
  
 _”Then on this day, I, Odin All-Father, proclaim you King of Asgard and all the Nine Realms.”_

 

***

  
  
Or to know what a few different words could change.  
  
 _”So I am nothing more than another stolen relic, locked up until you might have use of me?”_  
 _“Why do you twist my words?”_  
 _“You could have told me what I was from the beginning. Why didn’t you?”_  
 _“You are my son. I wanted only to protect you from the truth.”_  
 _“Because I’m the monster parents tell their children about at night?”_  
  
 _There was a silence as Odin steadied himself against the wall, feeling weaker by the second._  
  
 _“Loki,” he said, voice weak, “I have loved you ever since I chose you. Does that mean nothing? Do years of love and comfort-“_  
 _“Years of deception!” Loki countered._  
 _“I did what I had to do to see you safe. You were only an infant, left for dead. I could not have that on my conscience.”_  
 _“So it was pity, then,” Loki snarled._  
 _“Perhaps at first,” Odin admitted wearily. “But you have grown into as fine a prince as Asgard could ever hope for, and perhaps...”_  
  
 _He sighed._  
  
 _“Perhaps one day a king.”_  
  
 _Loki’s tears overflowed from his eyes. He shook his head, unable to look at his father._  
  
 _“I- Father, it was I who let the frost giants into Thor’s coronation,” he said in a miserable, gasping voice. “I tried to tell you before you banished him, but you wouldn’t listen-“_  
  
 _He looked up at Odin, wincing in anticipation of another burst of the All-Father’s fury and a swift trip to Midgard to join his brother, but Odin just looked... tired._  
  
 _This was potentially worse._  
 _“I’m sorry-“ Loki said desperately. “I didn’t think things would go this far-“_  
 _“Obviously not,” Odin said sternly._  
  
 _Loki stared at him. Odin glared back._  
  
 _After a moment, it was too much for Loki to take. He turned away from Odin and fell to his knees, sobbing._  
  
 _It was a very long time before he felt Odin’s hand settle on his shoulder._  
  
 _“Loki,” he said, “you have suffered enough for today.”_  
  
 _Loki glanced over his shoulder at where Odin stood and suppressed another sob._  
  
 _“Father-“_  
 _“There_ will  _be a consequence for your actions, Loki. But it will not be today.”_  
  
 _Loki stood up, legs shaking. He wiped a hand over his face._  
  
 _“I... I’m sorry, Father. If you need me to retrieve Thor, I swear I will-“_  
  
 _Odin’s eyes slid shut, and he collapsed on the stairs._

 

 

***

  
  
Or what difference one resisted temptation might make.  
  
 _”Mother- Mother, I can’t take the throne. I don’t deserve it. You’re the All-Father’s wife, you know better than anyone what to do-“_

 

 

 

***

 

  
  
Branches of spacetime formed dark mirrors of one another, until Loki and Thor stood facing one another Heimdall’s observatory.

“Thor,” Loki pleaded, “I’ve already done enough damage. Please consider what you’re  _thinking_ -“  
“I’m not thinking, Loki,” Thor snarled. “I’m  _doing_. That was always the difference between us.”  
“You can’t kill an entire  _race_ , Thor!” Loki shouted.  
“Why not?” Thor countered, pacing toward the center of the room. “What do you think Laufey will do if he learns you live still-“  
“He doesn’t have to know!” Loki insisted, voice growing hoarse. “None of this has to  _happen_  this way-“  
“ _Watch me._ ”  
  
Thor turned to continue powering up the world tree.  
  
“Once we’ve taken care of Laufey,” he announced, “we’ll worry about Odin. No one will  _ever_  hurt you like that again.”  
  
Thor turned around to try to toss Loki a casual, brotherly grin, but Loki was gone. He frowned.  
  
It was at that moment that something hit Thor hard enough to send him flying out of the observatory window and onto the Bifrost below.  
  
In a daze, he saw Loki appear beside him out of thin air, holding Gungnir.  
  
“You know,” Loki shouted over the wind, “this might be rather unorthodox, but I feel like now’s as good a time as any to point out that I think we’ve settled the magic vs brawn debate once and for all.”  
  
The Bifrost pulsed beneath them, knocking Loki to the ground as well. Thor looked out in the distance.  
  
“It’s already begun!” he shouted. “You can’t stop it- those monsters will  _pay_  for what they did to you-“  
“Oh, will you  _shut up!_ ” Loki snapped.  
  
And he struck the Bifrost with the tip of Gungnir.  
  
It was only a long, jagged crack at first. Thor stared.  
  
“What are you  _doing_?”  
“The right thing,  _for once_ -“  
  
The crack began to shudder and spread toward them. Loki instinctively grabbed Thor by the shoulder as the bridge began to sunder and fall before them.  
  
This was, of course, a very inconvenient time to remember how much Thor  _weighed_.  
  
“Hold onto my arm!” Loki bellowed. He was slipping forward as well, Gungnir lying uselessly beside him.  
  
Thor tried to climb up a little further, but the wind was howling around them and they were both being pulled.  
  
“I can’t-“  
“What is the meaning of this?” a voice shouted from behind where Loki stood.  
  
Odin had awoken.  
  
“Father,” Loki shouted, “ _please_ \- whatever else he might have done-“  
  
Odin grabbed Loki around the waist and pulled back as hard as he could.   
  
“ _You,_ ” Thor snarled. “Of course you’d save him again just to keep him in your clutches-“  
“Thor, for  _once_  can you actually think before you speak-“ Loki said through gritted teeth, still trying to drag Thor back up.  
“Loki,” Thor shouted back. “ _Brother._  Don’t you understand? I could have done it for you- I could have  _saved_  you-“  
“ _By killing my people!?_ ” Loki shouted in disgust.  
  
Thor stared up at him, suddenly placid and wide-eyed.  
  
He pulled one hand away from Loki’s arm.  
  
“Thor, you  _idiot-_  don’t you  _dare-_  Thor,  _no-_ ”  
  
Thor opened his other hand and fell silently into the void below.

 

 

 

***

 

In the first few hours, Loki reckoned he apologized for stealing Gungnir around seventy-five times, weeping into his mother’s shoulder. Frigga gently stroked his hair, the same way she had done for years when Loki was a child.  
  
He confessed that he had been the catalyst of the whole affair to the Lady Sif and the Warriors Three, but the uncomfortable understanding that whatever Thor had become was perhaps already there within him all along hung so heavily in the air between them that none of them had the inclination to respond with much vitriol, save a strike on the face from Sif.  
  
Loki felt he deserved that.  
  
Loki didn’t stay at the memorial feast for very long. While the other members of the royal household stayed behind to partake in celebrating the Thor they had known and loved, Loki found himself wandering into Heimdall’s observatory.  
  
“Can you see him anywhere?” he asked dully, rubbing the fingers of one hand over his newly fitted gold vambraces, engraved with a wing emblem. Thor’s emblem.  
“I’m afraid I can’t,” Heimdall responded.  
  
Loki looked out over the shattered end of the Bifrost and closed his eyes against tears.  
  
“And what of the mortal woman he encountered during his banishment?” he said, after a long silence.   
“She searches for him.”  
  
Loki’s mouth twisted.  
  
Perhaps, he thought, it would be better if Jane Foster never found him, or what he had become.


	2. Now

A thin beam of sunlight fell across the bed, illuminating the sleep-tangled limbs of the man and woman currently nestled into the sheets and making her skin seem to glow a delicate gold.  
  
His, on the other hand, was a vivid sky-blue.  
  
Lady Sif’s nose wrinkled as the sunlight touched her face. She sat up and scratched the back of her head and glanced down at Loki. She nudged him.  
  
Loki made an irritated noise and put a hand over his eyes. Sif elbowed him.  
  
Grief may have made strange bedfellows of them both, pushing them into finally accepting the childhood betrothal Odin and Heimdall had arranged for them long ago but which had spent years off the table once they had reached young adulthood, but that didn’t mean Sif had to act like she  _liked_  him.  
  
“Let me be,” Loki muttered.  
“It’s past noon. Get up,” said Sif.  
  
Loki frowned, still without opening his eyes.  
  
“I don’t want to get up,” he groaned.   
“Oh, please,” Sif scoffed. “We all know your beauty routine takes only as long as snapping your fingers.”  
  
This was enough to make Loki open his eyes and scowl at her. He had spent the year since Thor’s fall from the Bifrost trying to come to terms with his true appearance, learning to cast off the illusion of Asgardian skin in private until he felt comfortable enough with it to sleep and bathe in his natural shape. His runtiness may have made him a rather deformed and indecent specimen to the rest of the Jotnar, but it was an advantage among his adopted people. He was still of comparable size to the true-born people of Asgard, still of the proportions he had always had, still of the same features, just... blue. And covered in ridges, and with luminescent red eyes that rather defeated the point of rutting in the dark while he’d accustomed himself to his true body.  
  
For her part, Sif had already resigned herself to a not-yet-formalized eternity as Loki’s wife, and that prospect neither lost nor gained any charms if Loki happened to be blue in private. And deep down, it was harder to dislike Loki now than it had been a year ago. He’d  _changed_.  
  
For all that he was tormented by Thor’s absence and his own unintended hand in Thor’s spiral into madness, Loki had flourished in the last year, like a small plant finally able to bask in the sunlight when a mighty tree beside it is felled. In addition to his duties as heir apparent, he had devoted himself to quietly making amends for his past wrongs, and suffered his penances under a cover of simple mourning.   
  
“Fine,” he said, sliding one long leg over the edge of the bed and shading back to the pale Asgardian skin he wore in public life. “See? I’m up.”  
“You don’t want to keep the Vanir ambassador waiting, do you?” Sif asked, with heavy mock seriousness.  
“He’s not coming until the evening feast,” Loki grumbled.  
“I’ve watched how diplomacy works,” she countered, with a bright smile. “You’ll need at  _least_  an additional hour of kissing each other’s rear ends before you can even think about getting down to business.”  
  
Loki frowned, but it didn’t take. He pulled a robe over his nude body and went to prepare for the day.

 

***

 

After an hour of pleasantries and then another three of feasting, Loki was exhausted, despite the fact that almost nothing had been accomplished during the day. The Vanir embassy would be at court for the next week, which by near-necessity slowed the actual trade negotiations to a halt in order to give all the participants involved an opportunity to size one another up and seek out small weaknesses to exploit in sweetening the deals to be reached.  
  
It wasn’t that Loki wasn’t good at it. It was actually a talent he’d honed over several centuries, and one of great value when it came to maintaining the peace, especially with what Thor had tried to do to Jotunheim. It was more important than ever before to have a sharp tongue and quick wits, but the novelty of the situation was little comfort.  
  
Sif was still at the feast. Loki felt no desire to pressure her to retire to bed with him. He wandered in silence down to the palace vault, where Mjölnir, Thor’s hammer, still rested on a pedestal, as though Thor would come swaggering in the way he always had before to pick it up and give it a casual swing.  
  
It was enchanted now. No one would lift Mjölnir again until they proved  _worthy_ , whatever that meant.   
  
Loki’s hand closed over the handle of the hammer. He tugged on it.  
  
The hammer held fast.  
  
“Damn,” Loki muttered.  
  
He turned to leave, only to find himself facing the blue-robed figure of his mother, Frigga, standing at the bottom of the stairs.  
  
“I thought I might find you here,” she said, with a wry, sad smile.  
“I was only passing through,” said Loki.  
“Loki,” Frigga said as she approached him, opening her arms, “you mustn’t blame yourself.”  
  
Loki rounded his shoulders away from her, refusing her embrace.  
  
“Why not?” he said. “If I hadn’t-“  
“We’ve discussed this hundreds of times now,” Frigga replied, unyielding but loving. “It was a matter of the choices both of you made. You accepted your error, while Thor sought someone else to blame.”  
  
Loki slowly accepted her hand on his shoulder, turning just enough to look at her again. Frigga gently cupped his cheek in her hand.  
  
“And you have made both myself and your father proud,” she said.  
  
Frigga lead Loki back up the stairs. Loki stole one last glance back at Mjölnir on the way out.  
  
“I can’t shake the feeling that if things had worked out differently, I’d’ve done the same,” he muttered.  
“Don’t talk like that,” Frigga admonished him.  
  
Loki hunched his shoulders a little further in thought as he walked. Frigga smoothed a loose lock of his somewhat frizzy dark hair- he hadn’t taken the time to straighten it or stick it back since Thor’s fall- behind one of his ears, with a small sound of maternal approval  
  
Loki frowned at her sidelong. Frigga was smirking.  
  
“You may be the future king of Asgard,” she said, “but I’m still your mother.”  
  
Loki laughed a little, despite himself.

“Right,” he said wryly, “because there are  _so many_  reasons for you to take pride in that role, yes? Odin gave you  _such_  a choice in the matter.”  
  
Frigga’s expression hardened, but she said nothing, merely cast her eyes downward and continued walking.  
  
Loki sighed.  
  
“I’m sorry, Mother-“  
“I know you are,” said Frigga. “You always are.”  
  
Loki opened his mouth and shut it again as he tried to think of something to say, but nothing came to mind save that Thor wouldn’t’ve had this trouble if he were still with them. Thor could have glossed everything over with a smile and a kind word, but Loki’s skill with words extended only to those he needed to manipulate, never to those he ached to comfort. He averted his eyes from Frigga in return and was just beginning to hurry back to his chambers when there came a sound of clattering armor from around the corner that distracted both mother and son.  
  
One of Odin’s guards immediately dropped on one knee in salute before them.  
  
“Your Highnesses,” he said. “The Allfather requests Prince Loki’s presence in Heimdall’s observatory at once.”  
  
Loki frowned and looked to his mother in concern.  
  
“We’ll talk afterward,” Frigga said, touching his shoulder. “Your father needs you.”  
  
Loki nodded and hurried away with the guard. When he arrived in the observatory, Heimdall had a grave expression. Odin looked more tired than he’d looked in a year now, but also cold and angry. When he glanced up at Loki, it was enough to make Loki swallow hard and take a step back.  
  
“Y- yes?”  
  
He hung in the doorway like an anxious child, racking his brain for something, anything he might have done to displease the Allfather, but nothing came to mind. When Odin flapped a weary hand to beckon him closer, Loki was having trouble keeping himself from shaking.  
  
“Father, what is-“  
“Thor lives,” said Odin.  
  
Loki’s mouth dropped open. He now bolted toward Odin.  
  
“You found him? Where is he? Has his madness passed?”  
  
Odin looked up at Loki in grim silence. Loki frowned, trying to read his father’s expression.  
  
“...Father?”  
  
It was Heimdall who spoke instead, stepping around Odin to look Loki in the eye.  
  
“He’s on Midgard,” Heimdall said.  
“With the mortal woman?” Loki guessed.  
“I wish it were so,” said Heimdall, “but it is not.”  
  
Loki looked between them, a dire, sinking feeling in the pit of his stomach.  
  
“Thor has been seduced by forces of darkness,” Odin said quietly.


	3. SHIELD

**Notes for the Chapter:**

> This chapter is a freely adapted parallel to the opening scene in "The Avengers". As the story progresses, it'll be moving further and further from even a role-reversed adaptation of canon, but credit where it is due, etc.

_”Has the son of Odin been dispatched to the planet Earth?”_   
_“Yes, my lord. He has accepted your gift of the Stormhammer. An adequate replacement for what he has lost. His retrieval of the Tesseract is imminent. Our invasion force awaits his word.”_   
_“He has not forgotten the plan?”_   
_“No. Our errand before his vengeance, as ever before.”_   
_“I care not for his vengeance. The affairs of a petty godling are of no concern to me, only that which will be reaped in the wake of his despair.”_   
_“Of course, my lord. I mean only to say that his priorities remain arranged according to your wishes, rather glory or than his... fraternal sentiment.”_   
_“Good. Very good. And what of the humans?”_   
_“What chance have they against our power and that of a god?”_

_  
_***  
  
“Look at her,” Erik Selvig said in a fond coo, gazing down at a small glowing blue cube with all the tenderness of a new father. “Isn’t she  _something_.”  
  
For a moment, it looked almost as though Selvig were about to give the cube a little affectionate poke or a tickle, but he pulled himself at the last second and turned around to face his current supervisor.  
  
“I’m surprised Stark’s even letting us borrow her,” said Selvig, crossing back over to look at a row of monitors displaying the strange little cube’s behavior- which was, admittedly, not much at the moment. Not much that actually  _showed_  at any rate, beyond the fact that it was currently powering its own monitoring apparatuses.   
“You know how he gets,” replied Nick Fury, his own eye focused on the monitors as well. The Stark Industries logo gleamed ostentatiously in silver at the corner of each display. “The man has to be the bride at every wedding and the corpse at every funeral. It’s exactly that attitude that’s why he’s providing the tech and not on call to man the suit if we need him.”  
  
Selvig frowned.  
  
“I thought you had him on-“  
“That’s Col. Jim Rhodes,” Fury interrupted. “Rhodes is a military man. Good head on his shoulders, good at following orders, and doesn’t hire out half the Rockettes every time he has a press conference. They call him War Machine now.”  
  
Selvig shrugged. One man in a fantastic flying suit was much the same as another to him, and these days the concept itself sat pretty low on the scale of things that would impress him. A few hot summer days in New Mexico in the company of a Norse god would do that to a man- and were why Selvig was here in the first place, for that matter. He and his former protegée and now colleague, Jane Foster, had befriended a man calling himself Thor Odinson after Jane struck him with her car in the aftermath of an unusual lightning storm. Thor had turned out to have everything he needed to back up his claim save his trademark hammer and explained to Jane and Selvig that he needed their help to return to Asgard in order to save his brother from a terrible fate.   
  
While it didn’t make a lot of sense, Selvig, Jane, and Jane’s intern Darcy had happily obliged, returning Thor to his kingdom right before SHIELD had turned up to confiscate their equipment for further study. Once it was clear that they were as boggled as anyone else, however, they quickly found themselves on SHIELD’s payroll- Jane in New York, and Selvig still in New Mexico. He was called in due to their coming to be in possession of a piece of Asgardian technology, which Tony Stark was already developing into an energy source, and SHIELD was investigating further.

One of the monitors gave a sudden small chirp. Fury, Selvig, and a handful of the assembled staff glanced up toward it.  
  
Selvig held up a placating hand and rushed toward it as the machine gave another little noise. Then another, and another.  
  
“Is there something we should know about, doctor?” Fury asked slowly.  
“The energy output’s rising rapidly,” Selvig announced. “There doesn’t appear to be any  _cause_ -“  
  
The beeping gave way to a long high-pitched tone.  
  
“All right, everyone, evac procedure, that’s an order!” Fury shouted. Selvig hesitated amidst the rush of scientists and security personnel, and turned back just in time to see blue lightning come arcing down from the lab’s steel support rafters and converge on one spot.  
  
At first, Selvig assumed, running on pure instinct, that it had to be the cube that was attracting the lighting, until he realized that the cube was some ten feet behind him. There was an enormous electric crackle, a burst of light, and then-  
  
The lightning was gone, having left nothing but a burn mark on the ground, upon which stood the imposing blond figure of Thor Odinson, cloak fluttering behind him as the wind died down.  
Fury kept his gun raised in apprehension as Thor took a few measured, cautious steps away from where he’d landed. Selvig slowly emerged from under the table he’d been sheltering under.  
  
“...Thor?” he said.  
  
Thor turned to look at him in silence. His hair was longer than Selvig remembered, braided here and there, and he wore an enveloping deep red cloak, under which the vague shape of his hands could be determined, holding something in their grasp. His hammer, Selvig thought to himself.

“Thor, old man, good to see you-“  
  
He stopped short when he realized that Thor wasn’t returning his enthusiasm. Selvig took a step back while Thor continued striding forward. A look of recognition crossed Thor’s face as his eyes alighted on the cube.  
  
“Sir?” said Fury, though his tone was less one of respect and more of deeply concerned caution.  
“It was easier than I was lead to believe,” Thor murmured. He looked up at the humans and added, “I am sorry if this is a setback to your research.”  
  
He looked genuinely wounded and sincere, enough so that Selvig hazarded speaking to him again.  
  
“Thor... hey, what’s... what’s going on with you...”  
“I am here for the Tesseract,” said Thor, nodding at the cube.  
“For what purpose?” Fury said sharply.  
“I have made a promise,” Thor replied, “and I intend to honor it.”  
  
He gave a solemn-looking nod and reached one hand from within his cloak toward the Tesseract. Fury raised his gun and gestured for the others to do the same.  
  
“ _Sir_ ,” Fury said warningly.  
  
Thor stopped, hand a mere inch from the Tesseract, and glanced around the room.  
  
He smiled wearily.  
  
“Then you leave me no choice.”  
  
He swung something out from under his cloak, and Selvig saw that even if it was a hammer, it probably wasn’t Mjölnir. Mjölnir, for one, wasn’t more axe than hammer.  
  
“Thor-“  
  
Thor met Selvig’s eyes right as he swung the axe-hammer in a wide arc, releasing it from his hands and immediately decapitating an entire row of SHIELD paratroopers before they had a chance to fire on him as it flew through the air.  
  
“Holy  _shit-_ ” Fury shouted.  
  
Thor seized the Tesseract and began running while Fury shouted orders for the remaining paratroopers to fire. The scientists, on the other hand, were screaming and scattering away from their depowered workstations, and then immediately dodging- mostly unsuccessfully- the bullets that ricocheted harmlessly from Thor’s body.  
  
“Hey, big guy,” a voice shouted from above.  
  
Thor actually stopped just long enough to see a grim-faced man watching from an observation gallery who was drawing back an arrow aimed at him. Thor gave a furious roar and raised the axe-hammer again, this time to channel a long streak of blue lightning toward the man in the gallery, and not seeming to care when the man’s electrocuted corpse came tumbling over the edge.  
  
“We’ve got a hostile lifeform here,” Fury was saying into his walkie-talkie. “We have about sixteen- shit,  _Barton_ -  _seventeen_ agents down, this is a  _not a drill-_ ”

“Thor, for God’s sake!” Selvig shouted, running after him.  
“I have no quarrel with any of you,” Thor said, turning around to look at them again, “so long as you do not get in my way.”  
“You seem to have a pretty low threshold for what counts as ‘getting in the way’,” Fury retorted.  
“I came to retrieve the Tesseract, and I have. Let me conclude my mission in peace.”  
“Does this count as  _peace_  where you’re from?”  
“Let their deaths serve as a warning,” Thor said calmly.   
“Thor-“ Selvig began desperately. “What  _happened_  to you out there?”  
  
Thor laughed mirthlessly.  
  
“Nothing more than my duty,” he said.  
  
And with that, he held the hammer aloft and vanished again in a crack of blue lightning, leaving Fury and Selvig alone.  
  
“...I swear, sir, I had no idea-“ Selvig began.  
  
Fury turned around again to go back and assess the damage, finally allowing himself a sigh.  
  
“I’d better tell Romanoff myself before we start the established protocol,” Fury said darkly. “Call me crazy, but I’m pretty sure  _this means war_.”


End file.
